1. Field of the Invention
The present invention relates to a digital data processor, and particularly relates to a digital data processor which extends an N-bit quantized digital data signal to a quantized digital data signal having an M-bit width (M>N).
2. Description of the Related Art
In relatively new standards used for digital versatile discs (DVD), Blu-ray discs (BD) and the like, an audio signal can be recorded not only as a 16-bit quantized data signal like as a compact disc digital audio (CDDA), but as a 24-bit quantized data signal with higher accuracy. With the advanced standards for DVD and BD and the progress in hardware implementation techniques, an accuracy of an audio DA converter has been improved and 24-bit ICs for such purpose and also 32-bit ICs with further higher accuracy have appeared. On the other hand, CDs are still major media for musical packages and 16-bit quantization accuracy remains to be used in CDDA due to its standard. Hence, it is getting harder to say that the audio quality of CDs is sufficient as compared with the new standards used for DVDs, BDs and the like. For this reason, when quantization accuracy of data signal is not sufficient, it is required to virtually increase the number of quantization bits (quantization bit depth) of the audio data signal so as to improve its audio quality.
Under such circumstance, a technique disclosed in JP 2004-180017 A is known as a technique for extending the number of audio signal's quantization bits in audio signal processing. In the technique of JP 2004-180017 A, first, a change point from/to an increase (positive) to/from a decrease (negative) is extracted from a data waveform made up of a plurality of N-bit quantized data signals aligned along time series, and subsequently, a data waveform change mode, such as (positive, positive, positive, negative), is generated from a plurality of change points. Based upon the waveform change mode, a data waveform change pattern of M bits (N<M) is read from a table previously stored into a memory, and an original audio signal is replaced with it.